U.S. patent application number 15/087037 was filed with the patent office on 2017-10-05 for method and system for generating a received signal strength indicator (rssi) value that corresponds to a radio frequency (rf) signal.
This patent application is currently assigned to NXP B.V.. The applicant listed for this patent is NXP B.V.. Invention is credited to Jingfeng Ding, Gernot Hueber, Helmut Kranabenter, Stefan Mendel, Josef Zipper.
Application Number | 20170288795 15/087037 |
Document ID | / |
Family ID | 57995133 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170288795 |
Kind Code |
A1 |
Ding; Jingfeng ; et
al. |
October 5, 2017 |
METHOD AND SYSTEM FOR GENERATING A RECEIVED SIGNAL STRENGTH
INDICATOR (RSSI) VALUE THAT CORRESPONDS TO A RADIO FREQUENCY (RF)
SIGNAL
Abstract
Embodiments of a method and a system for generating a received
signal strength indicator (RSSI) value that corresponds to a radio
frequency (RF) signal are disclosed. In an embodiment, a method for
generating an RSSI value that corresponds to an RF signal involves
obtaining an attenuation factor code in response to applying an
automatic gain control (AGC) operation to the RF signal, obtaining
an analog-to-digital converter (ADC) code in response to applying
an ADC operation to a signal that results from the AGC operation,
and combining the attenuation factor code and the ADC code to
generate an RSSI value. Other embodiments are also described.
Inventors: |
Ding; Jingfeng; (Gratwein,
AT) ; Kranabenter; Helmut; (Graz, AT) ;
Mendel; Stefan; (Graz, AT) ; Hueber; Gernot;
(Linz, AT) ; Zipper; Josef; (Graz, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NXP B.V. |
Eindhoven |
|
NL |
|
|
Assignee: |
NXP B.V.
Eindhoven
NL
|
Family ID: |
57995133 |
Appl. No.: |
15/087037 |
Filed: |
March 31, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 17/318 20150115;
H04W 52/245 20130101; H03M 1/181 20130101; H04W 52/52 20130101 |
International
Class: |
H04B 17/318 20060101
H04B017/318 |
Claims
1. A method for generating a received signal strength indicator
(RSSI) value that corresponds to a radio frequency (RF) signal, the
method comprising: obtaining an attenuation factor code in response
to applying an automatic gain control (AGC) operation to the RF
signal; obtaining an analog-to-digital converter (ADC) code in
response to applying an ADC operation to a signal that results from
the AGC operation; and combining the attenuation factor code and
the ADC code to generate an RSSI value, wherein combining the
attenuation factor code and the ADC code to generate the RSSI value
comprises performing a bit shift operation on the attenuation
factor code and the ADC code, and wherein the number of bits of the
RSSI value is equal to the sum of the number of bits of the
attenuation factor code and the number of bits of the ADC code.
2. (canceled)
3. (canceled)
4. The method of claim 1, wherein performing the bit shift
operation on the attenuation factor code and the ADC code comprises
one of appending the attenuation factor code to the least
significant bit (LSB) of the ADC code and appending the attenuation
factor code to the most significant bit (MSB) of the ADC code.
5. The method of claim 1, wherein obtaining the attenuation factor
code comprises obtaining the attenuation factor code using a
programmable resistive voltage divider.
6. The method of claim 1, wherein obtaining the attenuation factor
code comprises obtaining the attenuation factor code using a
programmable capacitive voltage divider.
7. The method of claim 1, further comprising detecting a signal
envelope of the signal that results from the AGC operation.
8. The method of claim 7, further comprising buffering the signal
envelope.
9. The method of claim 8, wherein obtaining the ADC code comprises
converting the buffered signal envelope into the ADC code.
10. The method of claim 1, further comprising placing the RSSI
value into an RSSI lookup table.
11. A system for generating a received signal strength indicator
(RSSI) value that corresponds to a radio frequency (RF) signal, the
system comprising: an automatic gain control (AGC) device
configured to obtain an attenuation factor code in response to
applying an AGC operation to the RF signal; an analog-to-digital
converter (ADC) device configured to obtain an ADC code in response
to applying an ADC operation to a signal that results from the AGC
operation; and an RSSI device configured to combine the attenuation
factor code and the ADC code to generate an RSSI value, wherein the
RSSI device is further configured to perform a bit shift operation
on the attenuation factor code and the ADC code, and wherein the
number of bits of the RSSI value is equal to the sum of the number
of bits of the attenuation factor code and the number of bits of
the ADC code.
12. (canceled)
13. (canceled)
14. The system of claim 1, wherein the RSSI device is further
configured to append the attenuation factor code to the least
significant bit (LSB) of the ADC code or append the attenuation
factor code to the most significant bit (MSB) of the ADC code.
15. The system of claim 11, wherein the AGC device comprises a
programmable resistive voltage divider.
16. The system of claim 11, wherein the AGC device comprises a
programmable capacitive voltage divider.
17. The system of claim 11, further comprising a signal envelope
detector configured to detect a signal envelope of the signal that
results from the AGC operation.
18. The system of claim 17, further comprising a buffer configured
to buffer the signal envelope.
19. The system of claim 18, wherein the ADC device is further
configured to convert the buffered signal envelope into the ADC
code.
20. A method for generating a received signal strength indicator
(RSSI) value that corresponds to a radio frequency (RF) signal, the
method comprising: obtaining an attenuation factor code in response
to applying an automatic gain control (AGC) operation to the RF
signal; obtaining an analog-to-digital converter (ADC) code in
response to applying an ADC operation to a signal that results from
the AGC operation; appending the attenuation factor code to the
most significant bit (MSB) of the ADC code to generate an RSSI
value; and placing the RSSI value into an RSSI lookup table.
Description
BACKGROUND
[0001] Radio frequency (RF) communications devices typically need
to support a wide dynamic range. For example, an RF communications
device may need to cope with long distance communications with bad
coupling conditions as well as close distance communications with
good coupling conditions. Received signal strength indicator (RSSI)
values can be used to adjust an RF communications device to cope
with different communications conditions.
SUMMARY
[0002] Embodiments of a method and a system for generating an RSSI
value that corresponds to an RF signal are disclosed. In an
embodiment, a method for generating an RSSI value that corresponds
to an RF signal involves obtaining an attenuation factor code in
response to applying an automatic gain control (AGC) operation to
the RF signal, obtaining an analog-to-digital converter (ADC) code
in response to applying an ADC operation to a signal that results
from the AGC operation, and combining the attenuation factor code
and the ADC code to generate an RSSI value. Other embodiments are
also described.
[0003] In an embodiment, combining the attenuation factor code and
the ADC code to generate the RSSI value involves performing a bit
shift operation on the attenuation factor code and the ADC
code.
[0004] In an embodiment, the number of bits of the RSSI value is
equal to the sum of the number of bits of the attenuation factor
code and the number of bits of the ADC code.
[0005] In an embodiment, performing the bit shift operation on the
attenuation factor code and the ADC code involves one of appending
the attenuation factor code to the least significant bit (LSB) of
the ADC code and appending the attenuation factor code to the most
significant bit (MSB) of the ADC code.
[0006] In an embodiment, obtaining the attenuation factor code
involves obtaining the attenuation factor code using a programmable
resistive voltage divider.
[0007] In an embodiment, obtaining the attenuation factor code
involves obtaining the attenuation factor code using a programmable
capacitive voltage divider.
[0008] In an embodiment, the method for generating the RSSI value
that corresponds to the RF signal further involves detecting a
signal envelope of the signal that results from the AGC
operation.
[0009] In an embodiment, the method for generating the RSSI value
that corresponds to the RF signal further involves buffering the
signal envelope.
[0010] In an embodiment, obtaining the ADC code involves converting
the buffered signal envelope into the ADC code.
[0011] In an embodiment, the method for generating the RSSI value
that corresponds to the RF signal further involves placing the RSSI
value into an RSSI lookup table.
[0012] In an embodiment, a system for generating an RSSI value that
corresponds to a radio frequency (RF) signal includes an AGC device
configured to obtain an attenuation factor code in response to
applying an AGC operation to the RF signal, an ADC device
configured to obtain an ADC code in response to applying an ADC
operation to a signal that results from the AGC operation, and an
RSSI device configured to combine the attenuation factor code and
the ADC code to generate an RSSI value.
[0013] In an embodiment, the AGC device is further configured to
perform a bit shift operation on the attenuation factor code and
the ADC code.
[0014] In an embodiment, the number of bits of the RSSI value is
equal to the sum of the number of bits of the attenuation factor
code and the number of bits of the ADC code.
[0015] In an embodiment, the AGC device is further configured to
append the attenuation factor code to the least significant bit
(LSB) of the ADC code or append the attenuation factor code to the
most significant bit (MSB) of the ADC code.
[0016] In an embodiment, the AGC device includes a programmable
resistive voltage divider.
[0017] In an embodiment, the AGC device includes a programmable
capacitive voltage divider.
[0018] In an embodiment, the system further includes a signal
envelope detector configured to detect a signal envelope of the
signal that results from the AGC operation.
[0019] In an embodiment, the system further includes a buffer
configured to buffer the signal envelope.
[0020] In an embodiment, the ADC device is further configured to
convert the buffered signal envelope into the ADC code.
[0021] In an embodiment, a method for generating an RSSI value that
corresponds to an RF signal involves obtaining an attenuation
factor code in response to applying an AGC operation to the RF
signal, obtaining an ADC code in response to applying an ADC
operation to a signal that results from the AGC operation,
appending the attenuation factor code to the most significant bit
(MSB) of the ADC code to generate an RSSI value, and placing the
RSSI value into an RSSI lookup table.
[0022] Other aspects in accordance with the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrated by way of
example of the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 depicts a communications device in accordance with an
embodiment of the invention.
[0024] FIG. 2A depicts an embodiment of an AGC device of the
communications device depicted in FIG. 1 that is implemented as a
programmable resistive voltage divider.
[0025] FIG. 2B depicts an embodiment of an AGC device of the
communications device depicted in FIG. 1 that is implemented as a
programmable capacitive voltage divider.
[0026] FIGS. 3A-3D depict some embodiments of a buffer of the
communications device depicted in FIG. 1.
[0027] FIG. 4 depicts an example an RSSI value of an RSSI device of
the communications device depicted in FIG. 1.
[0028] FIG. 5A illustrates some results of ADC output and AGC
output with a small antenna.
[0029] FIG. 5B illustrates some results of ADC output and AGC
output with a large antenna.
[0030] FIG. 6 is a process flow diagram of a method for generating
an RSSI value that corresponds to an RF signal in accordance with
an embodiment of the invention.
[0031] Throughout the description, similar reference numbers may be
used to identify similar elements.
DETAILED DESCRIPTION
[0032] It will be readily understood that the components of the
embodiments as generally described herein and illustrated in the
appended figures could be arranged and designed in a wide variety
of different configurations. Thus, the following more detailed
description of various embodiments, as represented in the figures,
is not intended to limit the scope of the present disclosure, but
is merely representative of various embodiments. While the various
aspects of the embodiments are presented in drawings, the drawings
are not necessarily drawn to scale unless specifically
indicated.
[0033] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by this detailed description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
[0034] Reference throughout this specification to features,
advantages, or similar language does not imply that all of the
features and advantages that may be realized with the present
invention should be or are in any single embodiment of the
invention. Rather, language referring to the features and
advantages is understood to mean that a specific feature,
advantage, or characteristic described in connection with an
embodiment is included in at least one embodiment of the present
invention. Thus, discussions of the features and advantages, and
similar language, throughout this specification may, but do not
necessarily, refer to the same embodiment.
[0035] Furthermore, the described features, advantages, and
characteristics of the invention may be combined in any suitable
manner in one or more embodiments. One skilled in the relevant art
will recognize, in light of the description herein, that the
invention can be practiced without one or more of the specific
features or advantages of a particular embodiment. In other
instances, additional features and advantages may be recognized in
certain embodiments that may not be present in all embodiments of
the invention.
[0036] Reference throughout this specification to "one embodiment",
"an embodiment", or similar language means that a particular
feature, structure, or characteristic described in connection with
the indicated embodiment is included in at least one embodiment of
the present invention. Thus, the phrases "in one embodiment", "in
an embodiment", and similar language throughout this specification
may, but do not necessarily, all refer to the same embodiment.
[0037] FIG. 1 depicts a communications device 100 in accordance
with an embodiment of the invention. In the embodiment depicted in
FIG. 1, the communications device includes an automatic gain
control (AGC) device 102, a signal envelope detector 104, a buffer
106, an analog-to-digital converter (ADC) device 108, and an RSSI
device 110. The communications device is configured to process an
RF signal to generate a digital signal. The communications device
may be an integrated circuit (IC) device, such as an IC chip.
Although the illustrated communications device is shown with
certain components and described with certain functionality herein,
other embodiments of the communications device may include fewer or
more components to implement the same, less, or more functionality.
For example, in some embodiments, the communications device may
include at least one antenna 112 for the reception of RF signals.
In another example, in some embodiments, the communications device
may include a digital signal processing (DSP) device configured to
process digital signals.
[0038] The communications device 100 depicted in FIG. 1 can process
an RF signal to generate a digitalized version of the RF signal as
well as to generate an RSSI value representing the signal strength
of the RF signal. The RSSI value can be used to adjust the
communications device to cope with different communications
conditions, e.g., long distance communications with bad coupling
conditions as well as close distance communications with good
coupling conditions. For example, if the signal strength of the
received RF signal is low (e.g., as a result of large distance
communications with bad coupling conditions), the communications
device amplifies the received RF signal with a large amplifier
gain. If the signal strength of the received RF signal is high
(e.g., as a result of close distance communications with good
coupling conditions), the communications device amplifies the
received RF signal with a small amplifier gain or attenuates the
received RF signal. Consequently, the communications device 100
depicted in FIG. 1 can support a wide dynamic range (i.e., process
RF signals with a wide range of amplitudes). Compared to a
communications device that implements a separate RSSI measurement
device and does not use information gathered by AGC/ADC devices,
the communications device 100 depicted in FIG. 1 uses the AGC
device 102 and the ADC device 108 to generate RSSI values for
received RF signals. Consequently, the communications device 100
depicted in FIG. 1 can be implemented with fewer circuit components
and less substrate area (e.g., silicon area). In addition, compared
to a communications device that implements a separate RSSI
measurement device and does not use information gathered by AGC/ADC
devices, the communications device 100 depicted in FIG. 1 can
operate with less power consumption, which results in less energy
cost and less thermal emission.
[0039] The AGC device 102 of the communications device 100 is
configured to perform an AGC operation on an RF signal. The AGC
operation includes a signal attenuation operation in which the RF
signal is attenuated or a signal bypass operation in which the RF
signal is not attenuated. In some embodiments, the AGC device is
used to automatically attenuate an incoming RF signal from the
antenna if the RF signal is larger than a supply range and generate
an attenuation factor code that has M bits (where M is a positive
integer), which is output to the RSSI device for generating an RSSI
value. Without signal attenuation, an RF signal that is larger than
the supply range may be clipped by the signal envelope detector
104, resulting in an inaccurate signal strength measurement. In
some embodiments, the AGC device is implemented as a programmable
resistive voltage divider, a programmable capacitive voltage
divider, or a combination of a programmable resistive voltage
divider and a programmable capacitive voltage divider.
[0040] FIG. 2A depicts an embodiment of the AGC device 102 depicted
in FIG. 1 that is implemented as an M-bit programmable resistive
voltage divider 202. In the embodiment depicted in FIG. 2A, the
M-bit programmable resistive voltage divider 202 includes a first
resistor 226 with a fixed resistance and an M-bit controlled
resistor array 228 with a programmable resistance. The M-bit
controlled resistor array is controlled by an M-bit attenuation
factor code, which is output to the RSSI device for generating an
RSSI value. In an embodiment, the M-bit controlled resistor array
includes a number of resistors and each of the resistors can be
enabled or disabled (e.g., bypassed) by the M-bit attenuation
factor code to generate a particular resistance value. The M-bit
programmable resistive voltage divider receives an RF signal at an
input terminal 222 and outputs an output signal from an output
terminal 224. The output signal may be an attenuated version of the
received RF signal or identical to the received RF signal. In the
M-bit programmable resistive voltage divider depicted in FIG. 2A,
the first resistor is connected to the input terminal from which an
RF signal is received and the M-bit controlled resistor array is
connected to ground. Alternatively, the M-bit controlled resistor
array may be connected to the input terminal from which an RF is
received and the first resistor is connected to ground. The voltage
division ratio of the M-bit programmable resistive voltage divider
is adjusted by changing the resistance of the M-bit controlled
resistor array. The M-bit programmable resistive voltage divider
depicted in FIG. 2A is one possible embodiment of the AGC device
102 depicted in FIG. 1. However, the AGC device 102 depicted in
FIG. 1 is not limited to the embodiment shown in FIG. 2A.
[0041] FIG. 2B depicts an embodiment of the AGC device 102 depicted
in FIG. 1 that is implemented as an M-bit programmable capacitive
voltage divider 242. In the embodiment depicted in FIG. 2B, the
M-bit programmable capacitive voltage divider 242 includes a first
capacitor 236 with a fixed capacitance and an M-bit controlled
capacitor array 238 with a programmable capacitance. The M-bit
controlled capacitance array is controlled an M-bit attenuation
factor code, which is output to the RSSI device for generating an
RSSI value. In an embodiment, the M-bit controlled capacitor array
includes a number of capacitors and each of the capacitors can be
enabled or disabled (e.g., bypassed) by the M-bit attenuation
factor code to generate a particular capacitance value. The M-bit
programmable capacitive voltage divider receives an RF signal at an
input terminal 232 and outputs an output signal from an output
terminal 234. The output signal may be an attenuated version of the
received RF signal or identical to the received RF signal. In the
M-bit programmable capacitive voltage divider depicted in FIG. 2B,
the first capacitor is connected to the input terminal from which
an RF signal is received and the M-bit controlled capacitor array
is connected to ground. Alternatively, the M-bit controlled
capacitor array may be connected to the input terminal from which
an RF is received and the first capacitor is connected to ground.
The voltage division ratio of the M-bit programmable capacitive
voltage divider is adjusted by changing the resistance of the M-bit
controlled capacitor array. The M-bit programmable capacitive
voltage divider depicted in FIG. 2B is one possible embodiment of
the AGC device 102 depicted in FIG. 1. However, the AGC device 102
depicted in FIG. 1 is not limited to the embodiment shown in FIG.
2B.
[0042] Turning back to FIG. 1, the signal envelope detector 104 of
the communications device 100 is configured to detect the signal
envelope of an incoming signal. The signal envelope detector may
detect the maximum amplitude of a signal that is output from the
AGC device 102. In some embodiments, the signal envelope detector
is implemented as a sampling mixer with the same frequency as that
of the incoming signal. In these embodiments, the sampling mixer
may directly sample signal peaks or perform IQ sampling and
subsequently calculate the geometric sum. In some embodiments, the
signal envelope detector is implemented as a peak detector.
[0043] The buffer 106 of the communications device 100 is
configured to buffer or temporarily store the detected signal
envelope from the signal envelope detector 104. The buffer can be
used to prevent the ADC sampling kickback and to increase reverse
isolation. In some embodiments, the buffer is implemented as a
unity gain buffer, a fixed gain buffer, a transition gate, a
switch, or a combination of a unity gain buffer, a fixed gain
buffer, a transition gate, and/or a switch.
[0044] FIG. 3A depicts an embodiment of the buffer 106 that is
implemented as a unity gain buffer 306. In the embodiment depicted
in FIG. 3A, the unity gain buffer 306 includes an amplifier 308
having a first input terminal 310 used to receive the detected
signal envelope from the signal envelope detector 104 and a second
input terminal 312 that is connected to an output terminal 314 of
the unity gain buffer. The unity gain buffer depicted in FIG. 3A is
one possible embodiment of the buffer 106 depicted in FIG. 1.
However, the buffer 106 depicted in FIG. 1 is not limited to the
embodiment shown in FIG. 3A.
[0045] FIG. 3B depicts an embodiment of the buffer 106 that is
implemented as a fixed gain buffer 316. In the embodiment depicted
in FIG. 3B, the fixed gain buffer 316 includes an amplifier 318, a
first resistor 320, and a second resistor 322. The amplifier
includes a first input terminal 324 used to receive the detected
signal envelope from the signal envelope detector 104 and a second
input terminal 326 that is connected to ground through the first
resistor and connected to an output terminal 328 of the fixed gain
buffer through the second resistor. The fixed gain buffer depicted
in FIG. 3B is one possible embodiment of the buffer 106 depicted in
FIG. 1. However, the buffer 106 depicted in FIG. 1 is not limited
to the embodiment shown in FIG. 3B.
[0046] FIG. 3C depicts an embodiment of the buffer 106 that is
implemented as a transition gate 336. In the embodiment depicted in
FIG. 3C, the transition gate 336 includes an input terminal 338
used to receive the detected signal envelope from the signal
envelope detector 104 and an output terminal 340 from which the
buffered signal envelope is output. The transition gate depicted in
FIG. 3C is one possible embodiment of the buffer 106 depicted in
FIG. 1. However, the buffer 106 depicted in FIG. 1 is not limited
to the embodiment shown in FIG. 3C.
[0047] FIG. 3D depicts an embodiment of the buffer 106 that is
implemented as a switch 346. In the embodiment depicted in FIG. 3D,
the switch 346 includes an input terminal 348 used to receive the
detected signal envelope from the signal envelope detector 104, a
switching device or switching mechanism 350, and an output terminal
352 from which the buffered signal envelope is output. In some
embodiments, the switch can be implemented as a semiconductor
device, such as a field-effect transistor (FET) device. The switch
depicted in FIG. 3D is one possible embodiment of the buffer 106
depicted in FIG. 1. However, the buffer 106 depicted in FIG. 1 is
not limited to the embodiment shown in FIG. 3D.
[0048] Turning back to FIG. 1, the ADC device 108 of the
communications device 100 is configured to convert an analog signal
into a digital signal. In some embodiments, the ADC device converts
the buffered signal envelope from the buffer into an N-bit (where N
is a positive integer) ADC code, which is output to the RSSI device
for generating an RSSI value. Examples of the ADC device include,
without being limited to, a direct-conversion ADC, a
successive-approximation ADC, a ramp-compare ADC, a delta-encoded
ADC and a sigma-delta ADC.
[0049] The RSSI device 110 of the communications device 100 is
configured to obtain an RSSI value based on the attenuation factor
code from the AGC device 102 and the ADC code from the ADC device
108. The RSSI value generated by the RSSI device may be used to
control an electronic device, such as an amplifier. For example,
the RSSI value generated by the RSSI device is used to control the
gain of an amplifier within a receiver device or a transmitter
device. When the distance is close enough between a reader and a
contactless card, the gain of a card receiver can be decreased to
avoid card receiver saturation and the transmitting power of a card
transmitter can be decreased to avoid card receiver saturation.
When the distance is far away between a card reader and a
contactless card, the gain of a card receiver can be increased to
achieve better sensitivity and the transmitting power of a card
transmitter can be increased to achieve a larger communication
distance.
[0050] In some embodiments, the RSSI device 110 switches
automatically between two operating ranges. In an AGC operation
range in which the field induced voltage is larger than a certain
value (e.g., the voltage at RXP/RXN of the AGC device 102 is above
1.2 volts), the AGC device operates to attenuate an RF signal. The
voltage division ratio can be controlled by an M-bit attenuation
factor code until a targeted voltage is reached. The M-bit
attenuation factor code is used to calculate the incoming signal
strength. Within a communications device having a specific antenna
and matching system, the relationship between the signal field
strength and the induced voltage may be fixed such that the RSSI
value can be mapped inside of a lookup table with signal field
strength. In an ADC operation range in which the field induced
voltage on RX is smaller than a certain value, the AGC device does
not perform signal attenuation (attenuation factor code being 0),
and the ADC code can be used to evaluate the received field
strength value.
[0051] In some embodiments, the RSSI device 110 combines an M-bit
attenuation factor code and an N-bit ADC code to generate an RSSI
value of M+N bits. For example, the RSSI device may perform a bit
shift operation to append the M-bit attenuation factor code to the
lowest bit (e.g., the least significant bit (LSB) bit) of the N-bit
ADC code or to append the M-bit attenuation factor code to the
highest bit (e.g., the most significant bit (MSB) bit) of the N-bit
ADC code.
[0052] FIG. 4 depicts an example an RSSI value of the RSSI device
110 of the communications device 100 depicted in FIG. 1. In the
example depicted in FIG. 4, the RSSI device appends a 10-bit
attenuation factor code 450 to the highest bit of a 6-bit ADC code
460 to generate an RSSI value 470 of 16 bits. For example, the RSSI
device appends a 10-bit attenuation factor code of "0000000001" to
the highest bit of a 6-bit ADC code of "111000" to generate a
16-bit RSSI value of "0000000001111000." In another example, the
RSSI device appends a 10-bit attenuation factor code of
"0000000000" to the highest bit of a 6-bit ADC code of "111111" to
generate a 16-bit RSSI value of "0000000000111111." The RSSI values
can be used to adjust the communications device or other
communications device operably connected to the communications
device in response to communication conditions.
[0053] The RSSI device 110 may place a generated RSSI value in a
lookup table for a targeted antenna and matching setting. The
lookup table can be generated by different algorithms with
different sizes. In some embodiments, the RSSI device generates a
lookup table directly with each M-bit attenuation factor code and
each N-bit ADC code, resulting in a lookup table size of 2.sup.M+N.
In some embodiments, the RSSI device generates a lookup table for
the M-bit attenuation factor code and a lookup table for the N-bit
ADC code, resulting in a total lookup table size of
2.sup.M+2.sup.N. In some embodiments, the RSSI device uses an
interpolating method to reduce the lookup table. For example, the
RSSI device selects one or more of the M-bit attenuation factor
codes and the N-bit ADC codes to generate a lookup table. In some
embodiments, the RSSI device uses a polynomial curve fitting method
to reduce the size of a lookup table. For example, the ADC code can
be characterized by a 3 point linear curve,
y=ax+b (1)
where x represents the input voltage or the field strength,
parameters a and b are saved in the lookup table. The attenuation
factor code can be characterized by 3 order polynomial
equation,
y=ax.sup.3+bx.sup.2+cx+d (2)
where x represents the input voltage or the field strength,
parameters a, b, c, d are saved in the lookup table. In some
embodiments, an input voltage/field strength curve is calculated as
follows. In the ADC range (AGC=0, no attenuation), the input
voltage/field strength can be expressed as:
V.sub.IN=V.sub.LSB*N (3)
where V.sub.IN represents the input voltage/field strength,
V.sub.LSB represents a unit ADC least significant bit (LSB)
voltage, and the ADC device 108 has N bits. In the AGC range, the
input voltage/field strength can be expressed as:
V.sub.IN=V.sub.LSB*N*Att.sub.M (4)
where V.sub.IN represents the input voltage/field strength,
V.sub.LSB represents a unit ADC LSB voltage, Att.sub.M represents
the nominal attenuation factor code, and the ADC device has N bits.
After the input voltage curve is generated, a linear fit curve
between the true input voltage and typically calculated curve can
be calculated. The RSSI device can use a second order polynomial
curve (y=ax.sup.2+bx+c) for the attenuation factor code and a first
order linear curve (y=ax+b) for the input voltage
[0054] In an example operation of the communications device 100,
the AGC device 102 obtains an attenuation factor code in response
to applying an AGC operation to an RF signal. The ADC device 108
obtains an ADC code in response to applying an ADC operation to a
signal that results from the AGC operation. The RSSI device 110
combines the attenuation factor code and the ADC code to generate
an RSSI value that corresponds to the RF signal.
[0055] FIG. 5A illustrates some results of ADC output and AGC
output with a small antenna and FIG. 5B illustrates some results of
ADC output and AGC output with a large antenna. As shown in FIGS.
5A and 5B, there is no overlap between the AGC operation range and
the ADC operation range for small and large antennas. Consequently,
the communications device 100 can seamlessly switch between the AGC
operation range and the ADC operation range.
[0056] FIG. 6 is a process flow diagram of a method for generating
an RSSI value that corresponds to an RF signal in accordance with
an embodiment of the invention. At block 602, an attenuation factor
code is obtained in response to applying an AGC operation to the RF
signal. At block 604, an ADC code is obtained in response to
applying an ADC operation to a signal that results from the AGC
operation. At block 606, the attenuation factor code and the ADC
code are combined to generate an RSSI value.
[0057] In the above description, specific details of various
embodiments are provided. However, some embodiments may be
practiced with less than all of these specific details. In other
instances, certain methods, procedures, components, structures,
and/or functions are described in no more detail than to enable the
various embodiments of the invention, for the sake of brevity and
clarity.
[0058] Although the operations of the method(s) herein are shown
and described in a particular order, the order of the operations of
each method may be altered so that certain operations may be
performed in an inverse order or so that certain operations may be
performed, at least in part, concurrently with other operations. In
another embodiment, instructions or sub-operations of distinct
operations may be implemented in an intermittent and/or alternating
manner.
[0059] It should also be noted that at least some of the operations
for the methods described herein may be implemented using software
instructions stored on a computer useable storage medium for
execution by a computer. As an example, an embodiment of a computer
program product includes a computer useable storage medium to store
a computer readable program.
[0060] The computer-useable or computer-readable storage medium can
be an electronic, magnetic, optical, electromagnetic, infrared, or
semiconductor system (or apparatus or device). Examples of
non-transitory computer-useable and computer-readable storage media
include a semiconductor or solid-state memory, magnetic tape, a
removable computer diskette, a random access memory (RAM), a
read-only memory (ROM), a rigid magnetic disk, and an optical disk.
Current examples of optical disks include a compact disk with read
only memory (CD-ROM), a compact disk with read/write (CD-R/W), and
a digital video disk (DVD).
[0061] Alternatively, embodiments of the invention may be
implemented entirely in hardware or in an implementation containing
both hardware and software elements. In embodiments which use
software, the software may include but is not limited to firmware,
resident software, microcode, etc.
[0062] Although specific embodiments of the invention have been
described and illustrated, the invention is not to be limited to
the specific forms or arrangements of parts so described and
illustrated. The scope of the invention is to be defined by the
claims appended hereto and their equivalents.
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